Springback In Process Research Articles

Predictive and control models of the spring-back in thick hull plate forming

Hull complex plates are multidimensional curvature plates. It is difficult to adopt the traditional hot-forming method to process doubly or multiple curved plates. Multi-point forming automation equipment is a new forming process for 3D ship hull plate. However, the loading punches of traditional multi-point forming equipment are often designed in the point contact, which is easy to cause a series of defects, such as local indentations and wrinkle defects. The improved multi-point forming model with surface contact was proposed and verified with test methods. Moreover, the cold-forming process and spring-back process were simulated and analyzed with FEM for the improved multi-point forming model. The validity of the numerical method was confirmed by a series of experimental results. Finally, to ensure the forming precision, the successive approximation method was developed and verified to control the spring-back in cold-forming for curved hull plates.

Numerical and experimental analysis on cold-forming and spring-back of hull plate

Ship hull structures are fabricated by curved thick plates before they are welded together. There are traditional methods such as, line heating and laser-forming methods for plate bending. However, it is recognized that the hot-forming technology causes a series of troubles on doubly or multiple curved plates. Multi-point forming mechanism with square press heads is a new forming process for three-dimensional ship hull plate. Cold-forming has a high dimensional accuracy but results in spring-back. The spring-back process of curved thick plates in the finite element method is analyzed and the predicted results are compared with the test results in the present paper. To ensure the forming precision, the successive approximation method is also developed and verified to control the spring-back.

Experimental and numerical study on one flexible incremental bending process

In the shipbuilding industry, the traditional manufacturing method for the complicated ship hull metal plates is line heating method, which is not only labor intensive but also inefficient. Considerable efforts have been taken to develop the new automated manufacturing processes at a reasonable quality, efficiency and price during the last few decades. This paper presents a novel flexible forming process called incremental bending to achieve complicated plates. In this method, the initial metal plate is supported by some rotatable hydraulic cylinders and the punches move according to the given path, which is decided by minimum energy method and springback compensation method, to achieve the final plate. Taking one variable curved metal plate as one example, this paper investigates the formability of this novel process based on experiment and numerical simulation. During the numerical simulation, the implicit method is used and the gravity of the plate is considered mainly for the automatic positioning of the plate during each springback process. Results show that the incremental bending process can achieve variable curved metal plates with good accuracy, high efficiency, and relatively small punch load. In comparison with the existing methods, the new process has greater potentiality in the ship hull manufacturing industry.

Spring-back analysis in the cold-forming process of ship hull plates

Hull structures and offshore structures are composed of curved thick plates. Line heating method has traditionally been used to produce such curved plates. However, it is recognized that the hot-forming process causes a variety of issues on doubly or multiple curved plates. A multi-point forming mechanism with square press heads is a new forming process for 3D ship hull plate. Cold working has a high dimensional accuracy but results in spring-back. In this paper, the cold-forming process using explicit dynamic finite element method (FEM) and its spring-back process using implicit FEM were analyzed, and the impact of curvature and thickness on spring-back of hull plates was discussed. Moreover, the validity of the numerical method was confirmed by comparison with experimental results.

Resilient collapse of thermal sensitive polymer on the surface of the optical fiber taper

ABSTRACTIn this work, collapse of poly(N‐isopropyl‐acrylamide) (pNIPAM) grafted on the surface of the optical fiber taper is probed by measuring fluorescence of rhodamine B solution at various temperatures. It is observed that the fluorescence intensity through the taper shows a nonlinear response to temperature. According to the optical model for the special designed taper, it is realized that the nonlinear response results from changing in effective refractive index of interfacial layer between taper and solution. Analysis on relationship between signal change and collapse process reveals a springback process during the collapse of pNIPAM chains. Such a novel phenomenon is further investigated on method for fluorescence measurement and molecular weight of the polymer. These results have not only revealed details of the collapse, but also establish a novel technique for study the collapse of thermal sensitive polymers on the surface. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 778–785

A Review on Spring Back and Optimization Process

A Review on Spring Back and Optimization Process

Experimental study of springback behavior in incremental bending process

Manufacturing complicated and thick ship-hull plates at reasonable price and efficiency has always been a challenge in shipbuilding industry. One widely used method is line heating process, which is not only labor intensive but also ineffective. Recently many flexible forming processes have been developed while they all have avoidable disadvantages. In order to reduce the forming force, our group proposed one flexible incremental bending technology, during which the flat blank was bended into the required shape by gradually stamping at various positions. During the incremental bending process, the minimum energy method is used to determine the proper loading path. However, there is huge springback phenomenon after each bending. The shape change after each springback process should be considered in the loading path determination to make sure the accurate shape can be obtained.Here in this paper, the springback behavior of the carbon steel Q235 during the incremental bending process was investigated by experiments. In the first stage, the flat plates were bended several times at the same position while the final bending depth is the same, the final bending shapes after springback were compared to each other to investigate the influence of loading path on the springback behavior of the material. In the second stage, the flat plates were bended once at various positions and bending depths to study the springback behavior in one step bending process. It was found that loading path has little influence on the springback behavior, so during the incremental bending process, the springback law obtained from each single bending process can be used to combine with the minimum energy method to obtain the proper punch moving trajectory.

Study on cross-sectional deformation of rectangular waveguide tube with different materials in rotary draw bending

Abstract

Investigation of springback behavior and process control for stamping of ring-shaped workpiece

Due to the elastic deformation of metal stamping, springback is a serious problem to cause shape deviation and thus reduce precision. The springback behavior of ring-shaped workpiece is investigated in this paper and an auxiliary boss device is proposed to control the springback deformation. A finite element model is developed. The characteristic parameters including boss height, boss angle and boss gap are discussed systematically. It can be concluded that the gap has a positive linear correlation with springback percentage, and the boss angle has an optimal interval of 30 ◦ —60 ◦ to reduce springback. When the boss height increases, the springback decreases, but the effect weakens when the boss height is larger than 1.0 mm. Then, a response surface analysis is conducted with Design Expert 8.0.5 software and an optimal parameter process window (i.e., boss height from 2.1 to 3.0mm, boss angle from 53◦ to 60◦ and the gap from 0 to 1.2mm) is obtained. Finally, a set of molds are fabricated and the stamping experiments are conducted. The springback behavior is well controlled. The springback percentage can be decreased from 33% to 6% by using the auxiliary boss device of ring-shaped workpiece.

Meta-model Based Approach to Minimize the Springback in Sheet Metal Forming

Springback occurs at the end of sheet metal forming process where the geometric changes takes place in the part when the load is removed. It is an important factor to determine the quality of sheet metal forming. In this paper, the factors which affects the springback is determined and its influence over springback is studied analytically. The sheet metal forming process is performed using finite-element tool ABAQUS, so as to obtain the springback value for different process parameter. Punch radius and clearance gap along the horizontal axis between punch and die are the two process parameters considered for this study. For this study, 2D metal forming process has been performed and the springback angle is calculated at the corner area close to the holder. Kriging interpolation technique is used to build the surrogate model for the optimization process. Finite element method provides the data to build the metamodel which also helps in reducing the number of the real tests. Kriging or Gaussian process regression is an interpolation method which interpolates the values, modeled by a Gaussian process governed by prior covariance to optimize the smoothness of the fitted values. Kriging was applied to simulate the complex springback process. The sample data required to build the surrogate model was generated using MATLAB. Latin hypercube sampling technique has been utilized to generate the input sample points. The meta- model built with help of kriging interpolation for the sheet metal forming process is validated using RMSE method. With help of this approach we are able to predict the best process parameter which results in lower springback for the sheet metal forming is obtained, thereby reducing the spring back considerably. This paper gives a new approach that involves in reducing the springback phenomenon in sheet metal forming process with help of meta-model technique.

Bending Angle Prediction Model Based on BPNN-Spline in Air Bending Springback Process

In order to rapidly and accurately predict the springback bending angle in V-die air bending process, a springback bending angle prediction model on the combination of error back propagation neural network and spline function (BPNN-Spline) is presented in this study. An orthogonal experimental sample set for training BPNN-Spline is obtained by finite element simulation. Through the analysis of network structure, the BPNN-Spline black box function of bending angle prediction is established, and the advantage of BPNN-Spline is discussed in comparison with traditional BPNN. The results show a close agreement with simulated and experimental results by application examples, which means that the BPNN-Spline model in this study has higher prediction accuracy and better applicable ability. Therefore, it could be adopted in a numerical control bending machine system.

Stress and Springback Analyses of API X70 Pipeline Steel Under 3-Roller Bending via Finite Element Method

3-Roller bending is a widely applied manufacturing process, particularly in structural steel pipe industry. However, due to the difficulty and high cost of measuring stress distribution inside sheet material via traditional method, internal stress/strain response during forming is largely unexplored. The focuses of this study are two: (1) to map the radii of curvature as well as the stress inside the work piece during forming by utilizing the meshing mechanism of finite element method, and (2) to further provide some numeric guidelines for the configuration of the rolling system in order to improve production efficiency and product quality. The results of this study indicate that: (1) it is crucial to properly choose forming parameter in order to produce product with desired radii; (2) much like a gradual springback process, the radii of curvature gradually increase from the top roller to the exit-side bottom roller; (3) under the assumptions made in this study, to produce pipes with a specified diameter with varying configurations of the 3-roller system will not significantly change the final residual stress; and (4) finally, shifting of the neutral axis up to 2.0% of the thickness toward the compressing side during the forming process is observed.

Analysis of Residual Stresses Induced by Riveting Process and Fatigue Life Prediction

Residual stress induced by riveting process is critical to the fatigue life of riveted structures. A residual stress model is proposed to predict the residual stress distribution after riveting process. In the residual stress model, the radial pressure at the hole boundary is obtained, and the strain hardening effect of the rivet material is taken into consideration. The other characteristic of the model is that the solution of radial and circumferential residual stresses is extended to include an unfree springback process by using a springback coefficient. The residual stresses on the faying surface with various parameters, such as the height of the rivet drive head, the hole diameter, and the material property, are predicted with the residual stress model. The residual stresses calculated by the model are employed in the fatigue life prediction using the multi-axial fatigue criterion. The predicted results of the fatigue life show a good agreement with the experimental data. The investigation in this paper can help the residual stress prediction of riveted joints and improve the awareness of the effect of the residual stress on the fatigue behavior of riveted structures.

Benchmark 3 - Springback of an Al-Mg alloy in warm forming conditions

Accurate prediction of springback is a long-standing challenge in the field of warm forming of aluminium sheets. The objective of this benchmark is to predict the effect of temperature on the springback process through the use of the split-ring test [1] with an Al-Mg alloy. This test consists in determining the residual stress state by measuring the opening of a ring cut from the sidewall of a formed cylindrical cup. Cylindrical cups are drawn with a heated die and blank-holder at temperatures of 20, 150 and 240°C. The force-displacement response during the forming process, the thickness and the earing profiles of the cup as well as the ring opening and the temperature of the blank are used to evaluate numerical predictions submitted by the benchmark participants. Problem description, material properties, and simulation reports with experimental data are summarized.

Analysis and elimination for drum warpage of U-shaped workpiece with super length and large opening of sheet metal

To study the mechanism of workpiece warpage under air-bending forming, a method combined experiment with numerical simulation is proposed in this paper. Based on Hill’s yielding criterion and plane strain condition, 3D ABAQUS finite element models, used to form the semiellipse-shaped workpiece with super length and large opening of sheet metal, are established. The multistep incremental air-bending forming and non-uniform springback processes are simulated. It is pointed out that a large bending force and bed deformation of press brake can lead to warpage defect of workpiece. A technique used reverse deflection compensation for bed deformation of press brake, and female die with a large opening is found to eliminate warpage defect of workpiece. Manifested by the experiment for incremental air-bending forming of this workpiece, the proposed method yields satisfactory performance in improving forming accuracy and eliminating warpage defect of a large workpiece.

Springback prediction of three-dimensional variable curvature tube bending

The springback phenomenon of tube bending occurs consequentially after unloading, which will affect the manufacturing accuracy and processing efficiency of the tubular products. In this article, the bending and springback processes of minor-diameter thick-walled tube are simulated by ABAQUS to reveal the springback laws. The springback prediction of three-dimensional variable curvature bent tube is projected on each discrete osculating and rectifying plane, and then the three-dimensional problem can be transformed into two dimensions. The mathematic relationship of the radius before and after springback in the plane is built by approximate pure bending springback experiments. The springback on such planes is transformed into three dimensions. The tube axes are merged by first-order geometric (G1) continuity and then compensated with the modified function according to the axis complexity, so as to establish mathematic analytic model for springback prediction of three-dimensional variable curvature tube bending. Finally, the feasibility, reliability, and accuracy of the model are verified by finite element method and experiments.

Optimization of Parameters in Twist Springback Process for High-strength Sheets Based on Improved Particle Swarm Optimization Algorithm and Wavelet Neural Network

Optimization of Parameters in Twist Springback Process for High-strength Sheets Based on Improved Particle Swarm Optimization Algorithm and Wavelet Neural Network

Experimental and numerical studies on the warm deep drawing of an Al–Mg alloy

The warm deep drawing of circular AA5754-O aluminium alloy blanks was investigated both experimentally using specially designed equipment and numerically using a fully coupled thermo-mechanical finite element model. Cylindrical cups were prepared with a heated die and blank-holder. The split-ring test was used to measure the effects of the temperature on the springback process from room temperature to 200°C. Temperatures above 150°C were found to greatly affect the force/displacement response during the forming process and the ironing phase, the earing profile and the springback effect. Tensile and shear tests were also performed to study the temperature-dependent mechanical responses.To simulate this process, a temperature-dependent anisotropic model for the material was implemented in the commercial code ABAQUS/Standard, based on the UMAT interface for user-material models. The parameters of a phenomenological Hockett–Sherby hardening model and a power law strain rate dependency were identified using data obtained in uniaxial tensile and shear tests at various temperatures and strain rates, in order to account for both the temperature and the viscous effects in the coupled thermomechanical constitutive law. Von Mises isotropic criterion and Hill׳48 anisotropic yield criterion were also adopted to describe the material mechanical behaviour. The influence of the contact with friction conditions in the forming process (i.e. punch force evolution, thickness distribution along the cup wall and earing profiles) was also analysed. The numerical results obtained with the calibrated parameters generally showed a good match with the experimental temperatures. The results highlighted the importance of the correct choice of the yield criteria. The Hill48 criterion showed difficulties in the correct prediction of the springback process for this aluminium alloy.

Analysis on Stamping Forming Simulation and Springback Control of High-Strength Steel Auto-Body Panels

In recent years, the high-strength steel has been widely used in the automotive industry. As the high-strength steel sheet is prone to producing forming defects and serious springback problem in the stamping forming process, the finite element technique is used to simulate the value of stamping forming and springback process, so as to improve the stamping parameters and mold design according to the simulation results to achieve effective control of the springback value and efficiently improve the manufacturing precision of covering parts.

On twist springback prediction of asymmetric tube in rotary draw bending with different constitutive models

Springback and twist deformation of asymmetric AA6060-T4 aluminum tube in rotary draw bending process are studied experimentally and numerically. Of particular interest is the influence of constitutive model on the twist springback prediction results. The whole forming and springback process of this aluminum tube is performed using the finite element code ABAQUS. Several material models are analyzed, all considering isotropic and kinematic hardening combined with one of the following plasticity criterion: von Mises, Hill׳48 and Yld2000-2d. The material parameters of these constitutive models are determined from the tensile and forward-reversal shear tests of the tube. The material tests show that transient Bauschinger effect and curve crossing phenomena are observed for this tube subjected to reversal loading. The capability of two hardening model, naming isotropic and combined isotropic/ kinematic hardening model, to capture these behaviors are discussed. Comparison between the wist springback prediction results by different constitutive models shows that the springback angle is more sensitive to the hardening model while the twist deformation is more sensitive to the yield criterion. The stress distributions of the tube during different forming stages are analyzed and some explanations concerning their influence on springback mechanism are given. A detailed study on the tangent and hoop stress distributions of the tube also explains some source of the twist deformation for this asymmetric tube.